Laser video discs are one of the more useful high density information storage media commonly used today. Video discs store video and audio information in an arrangement which is fundamentally a digitized baseband composite television signal. In the United States, laser video discs store baseband representations of composite NTSC television signals including the luminance signal, the chroma signal modulated subcarrier, and the audio signal.
Commercially available video discs come in several sizes including a size mimicking the audio compact disc format, 8 inch and 12 inch diameters. Generally, the 12 inch video laser disc is considered the standard disc size. A standard 12 inch video disc stores 54,000 NTSC frames.
The construction of video disc playback equipment has become very sophisticated in recent years. Generally speaking, the playback apparatus of a video disc player includes a laser beam source and detector of reflected radiation, all carried on a traveler arm which moves radially over the surface of the video disc in a manner very similar to the movement of the magnetic heads over the surface of a magnetic disc used in a computer. The laser source illuminates the surface of the video disc over the area of a predetermined track. The digitized composite signal is stored by either the presence or absence of a burned light dispersing pit at predetermined intervals along the track. Most modern video disc players control the area of the disc illuminated by the laser by the use of precise stepping motors used to move the above referenced arm carrying the laser assembly radially over the disc surface. Also, servo controlled motors rotate the laser assembly and/or its optics about an axis parallel to a tangent to the disc. Therefore, stepping from frame to frame in a video disc player is accomplished by a combination of movement of the laser/optics assembly about the axis parallel to a tangent to the disc edge and moving the entire assembly radially over the surface of the disc.
This arrangement allows a number of advanced playback features in video disc players. Among the features are the familiar still frame action, in which a frame is constantly repeated so that a still image is provided to a video monitor receiving the reconstructed baseband signal. Additionally, slow motion can be accomplished by repeating the playback of each frame several time sequentially and then stepping to the next frame so that a clear image is achieved with an apparent slowing of motion.
As is known to those skilled in the art, the playback mechanisms commonly used for laser video disc lend themselves very nicely to storing large quantities of information on a frame by frame basis. In other words, rather than make the conventional use of stored television signals, that is providing a recording of moving pictures, video discs are well adapted to storing significant quantities of written and/or still pictorial information in each frame.
It is also well known that, as a result of the above described playback mechanism, video discs are, by their nature and the nature of the playback apparatus, suitable for being operated as either a random access playback device or a sequential access playback device. However, like magnetic disks on a computer, the random access operation of the video disc may be considered a quasi-random access. It is termed quasi-random access in the sense that the access time for any particular track of information on the disc's surface is a function of the distance between the current location of the playback transducer and the location of the track sought. However, the modern video disc playback apparatus is operated by stepping motors of sufficient precision so that any single frame of the disc may be individually sought and played back on a repeated basis, and the machine can be instructed to step from frame X to frame Y, where X and Y are any two numbers within the range of the number of frames stored on the disc.
While modern video disc playback equipment has many operational features in common, it is an unfortunate fact of the current state of technology and the consumer market for these products that there is no standardization with respect to control signals provided to a video disc playback apparatus which implement particular functions. Three generally stated levels of control of video disc playback are commonly recognized among those skilled in the art. Level 1 consists of typical television playback functions such as start, stop, scan forward, step to particular track, etc. These may be thought of as the type of playback functions typically provided in a home laser video disc system with a hand held controller for playing back recorded entertainment programs.
Level 2 of video disc playback control consists of a predetermined format of digital information stored on predetermined tracks of the video discs. With level 2 control, the digital control information is read from predetermined tracks at the beginning of playback and stored in a memory within the video disc player. Once this information has been loaded, the memory and a controller within the disc player control the sequence of playback operations according to the codes stored on the above referenced predetermined tracks.
Level 3 control represents interactive control through a control port connected to an external device.
While there is much commonality among playback functions which are implemented by video disc players, it is an unfortunate fact that there is no standardization of level 3 control among various manufacturers. In other words, the physical connectors and the electrical signaling schemes for providing level 3 control to video disc players is non-standard. Thus, the number of electrical conductors, or pins, at the control port of different players varies, as does the particular way in which the pins control the apparatus, and the electrical signaling protocols.
Among popular laser video disc playback devices currently available in the United States, there are three quasi-standard classes of level 3 control port provided by video disc player manufacturers. The first is serial communications implemented through a standard RS-232 serial port. The second quasi-standard is a bidirectional parallel latched 8 bit input/output port. This type of interface is one for which the controlling external device writes bits to the 8 bit parallel I/O port and reads certain bits from the port as acknowledgement signals or indications from the player as to its current status.
The third quasi-standard is a serial interface port using TTL logic levels and a dedicated acknowledge output line. This is one of the more troublesome type of control ports to deal with for standard serial communications devices. First, the logic levels are TTL rather than the standard 10 to 12 volt swing between 0 and 1 logic levels specified in RS-232. Second, the use of the acknowledge line alone provides only limited information as to the status of the player. Third, the waveform for these serial ports are non-standard. This type of control port has a dedicated acknowledge line which produces a particular logic level to acknowledge receipt of a command through the serial input line. The significance of the acknowledge command can vary depending on the command given to the player.
From this description it will be appreciated by those skilled in the art that there is a great diversity of electrical and signal protocol characteristics among the three quasi-standard types of level 3 control ports on commercially available video disc players.
Because of the quasi-random access nature of the video disc, it has become popular as a high density medium for storing teaching, training, and testing materials which may be operated by individuals at learning/testing stations consisting of a video disc player and a monitor for reproducing visual images corresponding to the recored composite signals. Such an arrangement is particularly useful for programmed instruction learning where the user is given a certain quantum of information, and then tested on his or her comprehension thereof by a short series of questions. The next sequence of images provided to the user in such an arrangement is determined by the user's responses to the previous questions, that is, the extent to which the user's responses indicated that they comprehended the previously provided information.
Designers of such instructional and testing arrangements can also opt for various responses of the machine, including making the user select answers until the right one is selected, or showing the user the correct answer and redisplaying the pertinent material in response to an incorrect answer.
Naturally, instructional and testing schemes of this type require a level 3 control to the video disc player. This is because the particular sequence in which the frames stored on the disc will be played back is not predetermined at the time playback commences. Since such testing schemes normally provide many possible branches along the way, there are a very large number of possible sequences of frame playback in such a system.
The need for level 3 control for practical instructional and testing apparatus, combined with the proliferation of various control signals and physical configurations for video disc player control ports, has lead to a situation in which most instructional and testing materials prepared for video disc playback systems are prepared only for a particular video disc size/format and for a particular video disc player. Furthermore, it will be apparent to those skilled in the art that general purpose programmable digital computers are very useful in providing the necessary level 3 control signals to the video disc player.
The fundamental problem with use of general purpose digital computers to provide level 3 control to video disc players for interactive operation thereof is expense and complexity. One of the basic advantages of using interactive video disc playback systems for instructional and testing purposes is the ability to provide a plurality of work stations at which a number of people may make use of the apparatus. This arrangement allows each user to proceed through the material in question at his or her own pace and obtain assistance based on user provided responses during the course of operation of the interactive device. Additionally, it allows the student to selectively repeat display of particular frames if they desire. However, by the very nature of the systems, the apparatus providing the interactive level 3 control to the video disc player must be duplicated at each station. Even as IBM PC compatible type machines have prices moving toward $1,000, they are still very expensive controlling devices.
Additionally, most personal computers which are used as the general purpose programmable digital computers to implement such controllers lack standard circuitry for conveniently producing TTL level serial ports and are thus limited in their ability to control the third type of quasi-standard interface described hereinabove without the use of additional circuitry. This requires a system implemented in this manner, which has the capability of controlling the third type of player control described above, to add the cost of additional custom circuitry on to the already large cost of the computer itself.
Furthermore, general purpose digital computers tend to be perceived as overly complex. This severely limits the usefulness of the apparatus used to implement interactive video disc instructions.
For example, many large companies or organizations will have television monitors available in a plurality of locations and it is highly desirable to be able to move the video disc player, a relatively small device, and the controller from one location to the other for use at different physical locations. The ability to practically do this is diminished by using general purpose digital computers for controllers. Because of this, interactive video disc instructional equipment has tended to be prohibitively expensive for many applications.
Furthermore, developers of course material have therefore tended to limit their materials to software instructions and discs which may only be played on a single playback system.
Additionally, it has generally been considered necessary to employ expensive general purpose digital computers in interactive video disc systems which display recorded information. Interactive video disc systems which can store records of the user response for later analysis are very useful in marketing surveys, point of sale response testing, and other activities in addition to the academic/instructional setting described hereinabove. Also, these machines are very useful in providing information stations at locations where people need directions, assistance, and the like.
Therefore, there is a serious need for an economical, lightweight and compact controller for providing level 3 control to video disc playback apparatus in interactive video systems which is usable to control a plurality of different types of video disc playback apparatus. In particular, there is a need for such a controller which provides transportability of the video disc and the control instructions defining the instructional or testing procedure among a plurality of different playback devices.